1. Field of the Invention
This invention is in the field of tennis rackets made up of essentially two channel-shaped members which have interengaging portions within their geometrics so that they can be received in tight interengaging relationship.
2. Description of the Prior Art
All are familiar with the conventional tennis rackets which for years have been made of wood and provided with gut or nylon strings. The playing characteristics of such wood rackets, however, unavoidably vary because of differences in the character of the wood, humidity and age. Such changes may tend to cause the head of the racket to warp due to variations in string tension.
The prior art is also replete with suggestions relating to steel and aluminum tennis rackets which do not have some of the noted disadvantages of the wood rackets but they are nevertheless difficult to fabricate and quite expensive.
The prior art also contains numerous disclosures, some of them quite incidental, dealing with the use of synthetic resins as materials for tennis racket manufacture, either alone or in combination with metal. The following discussion refers to some of such prior art disclosures but is meant to be illustrative only and is certainly not exhaustive.
In the late 1920's Robinson in his U.S. Pat. No. 1,636,867 disclosed a tennis racket which included a truss-type structure which could be utilized alone or embedded in a suitable material such as a "Bakelite" thermosetting resin. Panker U.S. Pat. No. 1,954,327 which issued in 1934 referred to a method of making tennis rackets by embedding a previously tightly stretched network in a frame consisting of a material which during embedding was rendered plastic and which hardened after being shaped to the desired shape to secure the strings firmly in position.
Hatton U.S. Pat. No. 2,274,788 issued in 1942 described a composite tennis racket in which a central metal tube was encased in a suitable plastic material such as a cellulose base material or a thermosetting resin.
Robinson U.S. Pat. No. 2,593,714 issued in 1952, describes in connection with FIG. 170 a method for manufacturing a tennnis racket in which plastic tubes are inserted into a prepared mold, utilizing tapered insert pins inserted between the opposed plastic tubes to form the stringing holes.
In more recent times, Eshbaugh in U.S. Pat. No. 3,483,055 which issued in 1969 described a method of producing tennis racket frames from flexible winding materials which involved the winding of such winding materials about a suitable form and then heat curing the materials to a rigid condition while under pressure.
Howe U.S. Pat. No. 3,690,658 described a tennis racket construction having a central dampening core sandwiched between skins of high strength material which served as the racket faces. The bow portion of the racket had at least one web having higher strength characteristics than the core, and extending normal to the skins, Layers of elastomeric material were utilized between the skins and the core to assist in laminating the core, skins and web into a unitary structure.
Erwin et al. U.S. Pat. No. 3,755,037 which issued in 1973 described a racket composed of a head portion and a handle portion integrally formed by a tubular member composed of helically wound fibers of high tensile strength embedded in a hardened binder having a preformed reinforcing member defining the base of the oval head portion and bounded on opposite sides to the tubular member, the handle portion being defined in part by generally parallel extending portions of the tubular member surrounded by a grip. The racket was produced by helically winding high strength fibers around the core, removing the core and finally hardening the binder.
Regardless of the method employed for making tennis rackets from synthetic resinous materials, the punching and drilling of string holes in volume production is quite an expensive procedure because of the costs of the tooling and the drilling time required. To our knowledge, no one had successfully molded in holes into a synthetic resin frame because of the complexity required in the mold.
The present invention overcomes the difficulty of the prior art and provides a tennis racket frame utilizing readily moldable parts having generally uniform wall thicknesses, the geometry of the parts being such that they can be identical in cross-section and by inverting one part with respect to the other, the various ribs and walls are made to engage with each other into firm integrated relationship.